1. Field of the Invention
The present invention relates to a method for actuating active vibration insulators which actively inhibit vibrations of vehicle engines from transmitting.
2. Description of the Related Art
As a conventional method for actuating such active vibration insulators, a highly linear actuator, such as a voice coil motor, for example, has been used to actuate an active vibration insulator with a sine-wave control signal, thereby controlling vibrations with great vibrating forces but with less noises. However, since such a high-performance actuator is highly expensive, it is difficult to use it in vehicles for which it is necessary to inhibit the vibrations of engines from transmitting simply and less expensively.
Moreover, as the other active vibration insulator, an electromagnetic vibrator has been known as disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 2001-117,644, for instance. The conventional electromagnetic actuator comprises an electromagnetic damper, and actuation controlling means. The electromagnetic damper comprises a fastener fitting, a yoke, a rubber elastic member, and a mass member. The fastener fitting is installed to a vehicle, a vibration generating force. The yoke accommodates an electromagnet therein, and is installed to the fastener fitting. The mass member is supported elastically to the yoke by the rubber elastic member. The actuation controlling means inputs electric control signals into the electromagnet of the electromagnetic damper, and lets the electromagnet generate actuating forces having magnitudes which correspond to the magnitudes of the electric control signals. Thus, the conventional electromagnetic actuator actuates the electromagnet to vibrate the mass member, thereby actively inhibiting the vibrations of the vibration generating source from transmitting by means of vibrating forces resulting from the vibrations of the mass member.
The conventional electromagnetic vibrator generates pulsating control signals with respect to rotary pulsating signals which are output from a rotary pulse sensor, for example, and whose frequencies are correlated to the vibration frequencies of the vibration generating source. Moreover, the pulsating control signals are synchronized with the rotary pulsating signals, but simultaneously have phases which are displaced with respect to the phases of the rotary pulsating signals. In addition, the pulsating control signals have control amplitudes which correspond to the vibration amplitudes of the vibration generating source and whose magnitudes are correlated to the magnitudes of duty ratios. Based on the pulsating control signals, the conventional electromagnetic vibrator gives vibrations to the mass member with the actuation controlling means, thereby inhibiting the vehicle from vibrating by means of vibrating forces resulting from the vibrations of the mass member.
However, when an engine is installed to a sub frame of vehicles, the conventional electromagnetic vibrator is installed to the sub frame as well.
Note herein that, when the conventional electromagnetic vibrator turns on or off the pulsating control signals, a secondary or tertiary harmonic signal component arises with respect to a datum frequency in the actuating signals for actuating the electromagnet. Moreover, when the frequency band of the secondary or tertiary harmonic signal component falls around the resonance frequency band of the sub frame, the secondary or tertiary harmonic signal component resonates to a vibration of the sub frame. Here, the phrase, “when the frequency band of the secondary or tertiary harmonic signal component falls around the resonance frequency band of the sub frame,” represents that a fundamental-wave signal component of control frequencies falls in a so-called idling range. That is, there occurs a problem that noises generate because the secondary or tertiary harmonic signal component resonates to a vibration of the sub frame in vehicles under idling. Note, however, that there occurs no such problem in vehicles under running where a fundamental-wave signal component of control frequencies has a high frequency.